U.S. Pat. No. 6,421,503 published Jul. 16, 2002 describes a heating system comprising two radiation members capable of emitting two different types of radiation. These radiation members are tubular in shape. The first radiation member comprises an incandescent filament capable of emitting a radiation in the near infrared range, whereas the second radiation member comprises a carbon ribbon capable of emitting a radiation in the medium infrared range.
It is a disadvantage of such a system that a given point of a coating under treatment is not simultaneously exposed to the two types of radiation. FIG. 1 is a cross-sectional view of such a heating system and of a coating treated by this heating system. The heating system shown in FIG. 1 corresponds to a heating system of FIG. 5 from U.S. Pat. No. 6,421,503. Such a heating system comprises a first radiation member 10 comprising a first quartz envelope 12 and a carbon ribbon 14, and a second radiation member 11 comprising a second quartz envelope 13 and an incandescent filament 15 kept in position by a support 15a. The two radiation members 10 and 11 are fixedly joined together by a central section 17. Each of the two radiation members 10 and 11 is covered with a reflecting layer 16 on an upper half of the respective quartz envelope 12 or 13.
Under these operating conditions, the radiation emitted by the first and the second radiation member 10 and 11 is necessarily downwardly directed when the heating system is arranged as shown in FIG. 1. Consequently, an object 18 to be treated by this heating system is present below said heating system. This object 18 comprises a coating 19 which is to be treated by the heating system. This may relate to, for example, a metal plate on which a paint comprising a pigment and a solvent has been deposited.
In such a configuration, the rays emitted by the radiation members 10 and 11 are not focused on the same location of the coating 19. As a result, the overlap of the two types of radiation, which is particularly advantageous in applications such as the drying of paints, is limited, i.e. the spectral combination of the spectra of the two types of radiation is limited.
In addition, the fact that the rays emitted by the radiation members 10 and 11 are not focused on the same location of the coating 19 leads to a prolonged treatment time for the coating 19, since each point of the coating 19 must be exposed to two types of radiation.
Another disadvantage of such a heating system is that the heating system is cumbersome. An oven for drying the coating will in fact generally comprise several heating systems arranged side by side, parallel to a direction in which the objects under treatment are moved. The dimensions of the heating system of FIG. 1 are important in view of this direction, because the heating system comprises two radiation members 10 and 11 arranged in this direction.